The final report concludes:(PDF 2,1 MB) Unused CERs conservatively amount to about 0.8-0.9 billion, about 40% of total issuance to date. The volume of CERs in the CDM registry alone reaches 0.4 billion. Regarding registration vintages, the bulk of unused CERs stems from activities registered before 2013. Therefore, all post 2013 options limit CER transition to well below 30 million. The host countries most vocal for unlimited CER transition are also those that have the highest volume of unused CERs to date. Africa would benefit quite strongly from a 2016 cut-off, given that is has achieved significant issuances from recently registered projects. Moreover, the study situates its findings in the broader context of the historical evolution of international carbon markets, their governance architecture and reporting and review processes, particularly regarding learning from past experiences under the CDM and improving the efficacy of the Paris Agreement market mechanisms under Articles 6.2 and 6.4. All in all, the study shows that all transition options and interests need to be carefully considered in the run-up to finalizing the design of Paris Agreement market mechanisms.